I'll freely admit I've yet to go to Lake Como but I've been to Lake Maggiore which lies to the north of Milan and along the border with Switzerland, so I am imagining it is very similar.
I really liked Lake Maggiore - we visited Stresa and from there took the ferry out to the three islands in the lake, visiting the gorgeous museum villas and terraced gardens and the small village on the third island. It was early July, the weather was perfect and the area was really beautiful and, most of all, tranquil. There were other tourists but it didn't feel crowded. Lake Maggiore likely attracts a bit less visitors than Lake Como.
I think the major difference between will be the setting itself and what you can do in each. I'd see Lake Como as a destination for relaxing, just walking around, strolling, eating good food, enjoying a boat ride into the lake. Cinque Terre is definitely more crowded - Rick Steves started promoting it, 15 years ago it
was "undiscovered" but that is no longer the case.
The lake area is much wider so visitors are spread out, the Cinque Terre are just five small towns sitting on the rocky cliffs between the mountains and the sea so space is limited so all visitors have to share the little space there is. I am sure in the summer Lake Como is also pretty crowded, it is when everyone has a chance to take time off and enjoy the nice weather.
We went back to Cinque Terre is April this year and it was perfect in terms of the number of visitors at that time. Vernazza was the most crowded and the difference was noticeable between there and Manarola and Riomaggiore.
Aside from the feeling of being crowded, I'd still go back to the Cinque Terre again and again for the incredible views!!
And the hiking

We love hiking so this personally attracts us to the Cinque Terre more than the lake district...
The path along the coast this year has been interrupted between Corniglia and Manarola because of landslides so instead we headed uphill to skirt the towns. Hardly anyone does that, so we felt we had the Cinque Terre to ourselves as we hiked between Riomaggiore and Monterosso on the crest trail - we might have seen a total of 10 people max. Even if you don't plan on hiking, you can enjoy the Cinque Terre very calmly by getting between each one with the train.
So whether you choose one for the other totally depends on what kind of things you'd like to do, although they are both destinations for enjoying nature and beauty!
